The present invention is directed to the field of equipment and accessories for processing semiconductor wafers. More particularly, it is directed to a receptacle and tool which are used to demount a semiconductor wafer from a carrier following one or more steps in a manufacturing operation.
During semiconductor manufacture, a semiconductor wafer undergoes a number of processing steps where it is exposed to potentially aggressive conditions including, but not limited to, chemical and physical contact, pressure, and temperature. These conditions may be deleterious to the features contained on the wafer or to the wafer itself. For example, the process of thinning a wafer for packaging, either by chemical or physical means, can result in wafer fracture. It is common, therefore, to mount the wafer to a carrier which provides support and stability to the wafer during processing. An adhesive means is commonly used to bond the wafer to the carrier to prevent slippage.
A wafer can be mounted to a carrier and retained in a number of ways. FIGS. 1a-1c show a semiconductor wafer partially adhered to a carrier by different adhesive means. FIG. 1a shows a wafer partially adhered using an adhesive layer such as epoxy or tape. FIG. 1b shows a wafer partially adhered using molecular Van der Waals forces. FIG. 1c shows a wafer partially adhered using a remote vacuum source. In each of these examples, the wafer exhibits a measurable deflection or strain due to the force of gravity acting on the unsupported area of the wafer. If the deflection exceeds a certain critical value, which depends on certain physical properties of the wafer, the wafer will fracture.
At the conclusion of a series of wafer processing steps the wafer must be debonded from the carrier. The debonding of the wafer must be done with care so as to avoid fracturing the wafer. The prior art includes a number of devices which can be used to demount a wafer from a surface. Typically these devices involve mechanical means that may impart damage to the wafer. Examples of wafer demounting devices include tweezers, blades, or vacuum wands.
Other devices have been developed which are less intrusive to the wafer. U.S. Pat. No. 5,952,242 to Pietsch discloses a means for removing a semiconductor wafer from a flat substrate in which liquid is used to lift the semiconductor wafer from the substrate. The fixture includes a cylindrical removal head which is mounted on a carrier disc and surrounds a wafer mounted thereon. The cylindrical removal head is provided with circumferential U-shaped grooves on an inner surface thereof to accommodate blocking devices which capture the wafer once it has been dislodged from the carrier disc. In this example, the wafer is merely resting on the carrier disc and is not adhered to the carrier by an adhesive means.
U.S. Pat. No. 4,466,852 to Beltz et al. discloses an apparatus and method for dislodging a wafer from a carrier by forcing a liquid through a channel passing through the disc. The liquid impinges on a back surface of the wafer at a point that is off-center so as to apply a leveraged force for loosening the wafer. The disclosure states that an operator manually catches the wafer as it is dislodged.
U.S. Pat. No. 4,949,783 to Lakios et al. discloses a substrate transport and cooling apparatus. Forced convection is provided by a gas flowing into the area between a substrate and a cooling fixture at a pressure high enough to cause bowing or lifting of the substrate and thus to create a gas region between the substrate and the fixture. An O-ring near the periphery of the substrate substantially seals the gas from entering a processing chamber. The gas flow into and through the area between the substrate and cooling fixture absorbs heat from, and thereby cools the substrate.
U.S. Pat. No. 5,632,847 to Ohno et al. discloses a method for removing a film from a substrate comprising injecting ozone in to an acid aqueous solution, and bringing bubbles formed by the ozone injection into contact with the film. When the ozone of each bubble is brought into contact with the film on the substrate, an intermediate between ozone and the film is formed, and then the formed intermediate is removed from the substrate by the acid aqueous solution of each bubble.
During the manufacture of gallium arsenide (GaAs) wafers, the wafer is typically bonded to a carrier. As seen in FIG. 2a, carrier 150 has a circular shape with an overall diameter s1. The carrier 150 is divided into two overall portions, an annular peripheral surface 152 of width s3 and a wafer support surface 154 having a radius s2.
The support region is populated with a pattern of through-holes 162. FIG. 2b shows the carrier 150 having a semiconductor wafer 170 adhered thereto by means of an adhesive 172. The wafer 170 is mounted on the top surface 174 of the carrier 150 at the wafer support surface 154, thereby leaving the peripheral surface 152 exposed. The carrier also has a back surface 176.
Given the brittleness of the semiconductor wafer 170 and the carrier 150, it is a challenge to dismount the wafer 170 from the carrier 150 without damaging either.
One device in accordance with the present invention comprises a wafer demount receptacle for removing a semiconductor wafer from a mounting carrier. The wafer demount receptacle includes a plate member that contains a pattern of through holes. The perimeter of the plate member comprises an upstanding rim structure which is stepped and includes a first step associated with a first riser and a first run, and a second step associated with a second riser. The run of the first step is shaped and sized to accommodate by abutment, a peripheral portion of a wafer carrier, to which a semiconductor wafer is bonded. When resting on the run of the first step, the wafer carrier is in an inverted orientation so that the semiconductor wafer rests in a space between the carrier and the plate member. The riser of the first step has a very low height so that the plate member limits the deflection of the wafer in a direction towards the plate member as the wafer is demounted from the carrier.
In one aspect of the invention, the wafer demount receptacle""s plate member is substantially circular, having a rim member including a first step defining a first diameter, and a second step defining a second diameter greater than the first diameter.
In another aspect of the invention, the wafer demount receptacle has unitary construction, being formed such as by casting or machining from a single piece of material. The material of construction may be any suitable material such as quartz or sapphire, but preferably is formed from stainless steel or alumina.
A second device of the present invention comprises a wafer demount gas distribution tool for removing a semiconductor wafer from a wafer carrier. The gas distribution tool comprises a gas shower head with a gas inlet port and a substantially flat external face having an operative gas distribution surface containing a pattern of through holes which serve as gas outlet ports. A peripheral sealing member provided around a perimeter of the operative gas distribution surface, helps form a seal between the operative gas distribution surface and an opposing surface against which the gas distribution tool is abutted.
In one aspect, the gas distribution tool""s operative gas distribution surface is substantially circular and the peripheral sealing member is a toroidal O-ring. With such a geometry, the gas distribution tool can be used in conjunction with the wafer demount receptacle for removing a semiconductor wafer from a wafer carrier. This is done by positioning the gas distribution tool with its operative gas distribution surface and O-ring juxtaposed against the back side of wafer carrier mounted in the wafer demount receptacle.
A first method in accordance with the present invention for debonding a wafer from a wafer carrier includes the steps of providing a wafer demount receptacle having an upstanding rim member, placing a wafer carrier in an inverted position such that a portion of the rim member supports a periphery of the wafer carrier, contacting the wafer carrier with a solvent to promote separation of the semiconductor wafer from the wafer carrier, whereby an edge of the semiconductor wafer first separates from the wafer carrier and the wafer partially rests on the plate member, and then a remaining portion of the semiconductor wafer separates from the wafer carrier such that the semiconductor wafer rests entirely on the plate member.
A second method in accordance with the present invention for debonding a wafer from a wafer carrier includes the steps of providing a wafer demount receptacle having an upstanding rim member, placing a wafer carrier in an inverted position such that a portion of the rim member supports a periphery of the wafer carrier with a semiconductor wafer mounted on the wafer carrier attached facing in a downward direction, contacting the wafer carrier with a solvent to promote separation of the semiconductor wafer from the wafer carrier, fully dissolving the adhesive, placing the operative gas distribution surface of the gas distribution tool in contact with the back surface of the carrier, flowing gas through the gas distribution tool, whereby gas bubbles are formed between the wafer carrier and the semiconductor wafer, an edge of the semiconductor wafer first separates from the wafer carrier and the wafer partially rests on the plate member, and then a remaining portion of the semiconductor wafer separates from the wafer carrier such that the semiconductor wafer rests entirely on the plate member.
In an aspect of either the first or the second method, the wafer carrier in abutment with the wafer demount receptacle is placed in a rack along with other such carrier/receptacle assemblies, and the rack is placed in a tank, prior to the step of contacting the wafer carriers with a solvent.